I'm a bit confused in regards to how EF's dbContext works.
If I do something like _context.Persons.Add(_person) (assuming person is a valid entity), if I then (before calling _context.SaveChanges()) query Persons, will the person I just added be included in the results?
For example:
Person _person = new Person() {Firstname = "Bill", Lastname = "Snerdly"};
_context.Persons.Add(_person);
var _personList = _context.Persons.Where(p => p.Lastname.StartsWith("Sne"));
Whenever I try this, it seems as though the context loses track of the fact that I've added this new person to the context.
What confuses me is that if I edit an existing person and attach the person and set the state to modified, querying the context seems to keep track of the changes that were made and returns them in the results. For example:
//Assuming that Person 5 exists with the name William Snerdly
Person _person = new Person() {Id = 5, Firstname = "Bill", Lastname = "Snerdly"};
_context.Persons.Attach(_person);
_context.Entry(_person).State = System.Data.EntityState.Modified;
var _personList = _context.Persons.Where(p => p.Lastname.StartsWith("Sne"));
In this case, it seems like the person with the id of 5 will show up in the list with the name Bill instead of William. IOW, the context queried the data but retained the changes while in the first scenario, the context queried the data but ignored any added items. It just seems a bit inconsistant.
Am I understanding this correctly or am I missing something?
Thanks for your help with this.
No, as it does not yet exist in the database. It will, however, be accessible through the ObjectStateManager of the ObjectContext, or alternatively, if you're using the DbContext/DbSet wrappers, through the .Local property of the DbSet.
In the case of the edit, you're seeing the ORM's first level cache at work. The query is executed against the database (and so compares against the values in there - your example would get even weirder if you modified the Lastname in the context, but still get the result from the query looking for the unmodified Lastname), but when its results are processed, first the ID of the returned entity is checked, and since the entity with that ID is already present in the context, you get that instance back. This is the default "AppendOnly" mode of operation.
I don't know what you want to do, but I had to understand all that when I wanted to validate my changes according to rules that needed to use the values of both loaded and unread entities. I ended up starting a transaction, saving the changes with the "None" options, doing my validation queries againt the database (which then contained the "merged" view of the data), and the rolling back the transaction if the data was invalid, or accepting the changes and committing the transaction otherwise.
Related
I'm having a strange issue.
I created a model observer for my user model. The model observer is being run at 'saving'. when I dump the object at the very end of the user model to be displayed ( this is just before it saves.. according to laravel docs ) it displays all the attributes set correctly for the object, I've even seen an error that showed the correct attributes as set and being inserted into my database table. However, after the save has been completed and I query the database, two of the fields are not saved into the table.
There is no code written by myself sitting between the point where I dumped the attributes to check that they had been set and the save operation to the database. so I have no idea what could be causing this to happen. All the names are set correctly, and like I said, the attributes show as being inserted into the database, they just never end up being saved, I receive no error messages and only two out of ten attributes aren't being saved.
In my searches I have found many posts detailing that the $fillable property should be set, or issues relating to a problem with variables being misnamed or unset, however because I already have the specific attributes not being saved specified in the $fillable array, on top of the fact that they print out exactly as expected pre save, I don't believe those issues are related to the problem I am experiencing.
to save I'm calling:
User::create(Input::all());
and then the observer that handles the data looks like this:
class UserObserver {
# a common key between the city and state tables, helps to identify correct city
$statefp = State::where('id',$user->state_id)->pluck('statefp');
# trailing zeros is a function that takes the first parameter and adds zeros to make sure
# that in this case for example, the dates will be two characters with a trailing zero,
# based on the number specified in the second parameter
$user->birth_date = $user->year.'-'.$user->trailingZeros( $user->month, 2 ).'-'.$user->trailingZeros( $user->day, 2 );
if(empty($user->city)){
$user->city_id = $user->defaultCity;
}
$user->city_id = City::where( 'statefp', $statefp )->where('name', ucfirst($user->city_id))->pluck('id');
# if the user input zip code is different then suggested zip code then find location data
# on the input zip code input by the user from the geocodes table
if( $user->zip !== $user->defaultZip ){
$latlon = Geocode::where('zip', $user->zip)->first();
$user->latitude = $latlon['latitude'];
$user->longitude = $latlon['longitude'];
}
unset($user->day);
unset($user->month);
unset($user->year);
unset($user->defaultZip);
unset($user->defaultCity);
}
that is the code for the two values that aren't being set, when I run
dd($user);
all the variables are set correctly, and show up in the mysql insert attempt screen with correct values, but they do not persist past that point.. it seems to me that possibly mysql is rejecting the values for the city_id and the birth_date. However, I cannot understand why, or whether it is a problem with Laravel or mysql.
since I was calling
User::create();
I figured I'd try to have my observer listen to:
creating();
I'm not sure why it only effected the date and city variables, but changing the function to listen at creating() instead of saving() seems to have solved my problem.
I have been struggling with an issue for a couple of days. I am sharing a Content Provider with two different apps (app A and app B). All the stuff regarding DB creation and Content Provider management is done by app A. App B just accesses it using the corresponding Authorities and a Content Provider Client.
ContentProviderClient myCPClient = this.miContext.getContentResolver().acquireContentProviderClient(this.miUri);
The problem comes up when trying to query the database in a more complex way, i.e. using some key words like GROUP BY, HAVING, etc. I need to get unique references according to one specific column (I want to use GROUP BY), and I have found out that there is no rawQuery() method for a ContentProviderClient, but a simplified query() method (compared to the one available in the class SQLiteDatabase, which allows to formulate proper MySQL commands).
I have checked this answer, but since my ContentProvider is accessed from a different app, I do not have any class like MyContentProvider.
To sum up, is there any way to make a proper query (like rawQuery()) to a ContentProvider which was generated by a different app?
I have finally got to a solution which is rather simple and sensible. I got a very good explanation about Content Providers and Content Resolvers. The latter is used to access the former, which means that they can not control what is in the provider, but get data from them. This means that you can not make a Content Provider Client to use a rawQuery() if it is not implemented (override) in the query() method of the corresponding ContentProvider.
To work around my problem, I have used a flag in my provider client and modify my content provider to read it so I can make use of GROUP BY. I just wanted to get unique references from the database according to a particular column.
Here it is the solution, which is not a very clean one, but it works quite well.
For the ContentProviderClient,
ContentProviderClient myCPClient = this.miContext.getContentResolver().acquireContentProviderClient(this.miUri);
//I declare some variables for the query
//'selection' will get all the rows whose "_id" is greater than 0, i.e. all the rows
String selection = BaseDatosParam.Tabla._ID + ">?";
String[] selectionArgs = {"0"};
//'groupBy' is not formatted in any particular way. I just need it to contain the pattern "GROUP BY"
String groupBy = "GROUP BY" + BaseDatosParam.Tabla.REF;
//the last field of the query corresponds to 'sortOrder', but I
Cursor c = myCPClient.query(Uri.parse(miUri.toString()),
projection, selection, selectionArgs, groupBy);
In the ContentProvider,
public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder)
{
String where = selection;
String groupBy = null;
SQLiteDatabase db = this.miBDManager.getWritableDatabase();
//We just check out whether 'sortOrder' includes the pattern "GROUP BY", otherwise that field will remain null
Pattern myPat = Pattern.compile("GROUP BY");
Matcher myMat = myPat.matcher(sortOrder);
if (myMat.find())
groupBy = myMat.replaceFirst("");
Cursor c = db.query(BaseDatosParam.Tabla.NOMBRE_TABLA, projection, where, selectionArgs, groupBy, null, null);
c.setNotificationUri(this.getContext().getContentResolver(), uri);
return c;
}
Regards,
I have a view ObjectDisplay that is composed of two relevant tables: Object and State. State represents the state of an Object, and the view pulls some of the details from the most recent State for each Object.
On the page that is displaying this information, a user can enter some comments, which creates a new State. After creating the new State, I immediately pull the Object from ObjectDisplay and send it back to be dropped into a partial view and replace the Object in the grid on the page.
// Add new State.
db.States.Add(new State()
{
ObjectId = objectId,
Comments = comments,
UserName = username
});
// Save the changes (executes all of the above).
db.SaveChanges();
// Return the new Object information.
return db.Objects.Single(c => c.ObjectId == objectId);
According to my db trace, the Single call occurs about 70 ms after the SaveChanges call, and it occurs on the same SPID.
Now for the issue: The database defaults the value of RecordDate in State to GETUTCDATE() - I don't provide the date myself. What I'm seeing is that the Object returned has the State's RecordDate of the old State and the Comments of the new State information of the old State. I am seeing that the Object returned has the old State's information. When I refresh the page, all the correct information is there, but the wrong information is returned in the initial call from the database/EF.
So.. what could be wrong? Could the view not be updating quickly enough? Could something be going on with EF? I don't really know where to start looking.
If you've previously loaded the same Object entity in the same DbContext, EF will return the cached instance with the stale values, and ignore the values returned from SQL.
The simplest solution is to reload the entity before returning it:
var result = db.Objects.Single(c => c.ObjectId == objectId);
db.Entry(result).Reload();
return result;
This is indeed odd. In SQL Server views are not persisted by default and therefore show changes in the underlying data right away. You can create a clustered index on a view with effectively persists the query, but in that case the data is updated synchronously, so you should see the change right away.
If you are working with snapshot isolation level your changes might not be visible to other SPIDs right away, but as you are on the same SPID and do not use snapshot isolation, this cant be the culprit either.
The only thing left at this point is the application layer. Are you actually using the result of the Single call higher up in the call stack or does that get lost somewhere. I assume that a refresh of the page uses a different code path, which would explain why it is working there.
We have the need to clone a complex data structure from one org to another. This contains a series of custom SObjects, including parents and children.
The flow would be the following. On origin org, we just JSON.serialize the list of SObjects we want to send. Then, on target org, we can JSON.deserialize that list of objects. So far so good.
The problem is that we cannot insert those SObjects directly, since they contain the origin org's IDs and Salesforce won't let us insert objects that already have Ids.
The solution we found is to manually insert the object hierarchy, maintaining a map of originId > targetId and fixing the relationships manually. However, we wonder if Salesforce provides an easier way to do such a thing, or someone knows a better way to do it.
Is there an embedded way in Salesforce to do this? Or are we stuck into a tedious manual process?
List.deepClone() call with preserveIds = false might deal with one problem, then:
Consider using upsert operation to build the relationships for you.
Upsert not only can prevent duplicates but also maintain hierarchies.
You'll need an external Id field on the parent, not on the children though.
/* Prerequisites to run this example succesfully:
- having a field Account_Number__c that will be marked as ext. id (you can't mark the standard one sadly)
- having an account in the DB with such value (but the point of the example is to NOT query for it's Id)
*/
Account parent = new Account(Account_Number__c = 'A364325');
Contact c = new Contact(LastName = 'Test', Account = parent);
upsert c;
System.debug(c);
System.debug([SELECT AccountId, Account.Account_Number__c FROM Contact WHERE Id = :c.Id]);
If you're not sure whether it will work for you - play with Data Loader's upsert function, might help to understand.
If you have more than 2 level hierarchy on the same sObject type I think you'd still have to upsert them in correct order though (or use Database.upsert version and keep on rerunning it for failed ones).
In LINQ-to-SQL if I update an object in the context but haven't called SubmitChanges, is there a way to "undo" or abandon that update so that the changes won't get submitted when I eventually call SubmitChanges?
For example, if I've updated several objects and then decide I want to abandon the changes to one of them before submitting.
Part 2: same question for Entity Framework, v3.5
Both LINQ to SQL and Entity Framework will use the same call (assuming you still have the active Context):
_dbContext.Refresh(RefreshMode.OverwriteCurrentValues, yourObj);
A more appropriate way would be to treat the Context as a Unit of Work, in which case you would no longer have an active context when refreshing the object. You would simply dispose of the object you're using currently and get a fresh copy from a new context.
I think you can use the .GetOriginalEntityState(yourEntity) to retrieve the original values. Then set your updated entity back to the original
dim db as new yourDataContext
//get entity
dim e1 as yourEntity = (from x in db.table1).take(1)
//update entity
e1.someProperty = 'New Value'
//get original entity
dim originalEntity = db.table1.getOrignalEntityState(e1)
e1 = originalEntity
db.submitChanges()
Very pseudo-code but I think it conveys the right idea. Using this method, you could also just undo one or more property changes without refreshing the entire entity.